The ionization chamber CC13-S is intended for relative dosimetry of photon, electron, and proton beams in radiotherapy. Measurements can be performed in air, water phantoms, or solid phantoms. The CC13-S is a high spatial resolution, small volume chamber. It is waterproof, vented through a waterproof sleeve, and fully guarded. It is designed for axial or lateral beam incidence and for the use in RFA-300 and RFA-200 phantoms only, using the grounded input technology.